1. Field of the Invention
The invention is generally related to the area of integrated circuits designs, and more particularly, related to improved designs of integrated circuits for high-speed signals and methods therefor.
2. The Background of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. Wavelength division multiplexing (WDM) is a technology that puts data from different sources together on an optical fiber with each signal carried at the same time on its own separate light wavelength. Using the WDM system, up to 80 or more separate wavelengths or channels of data can be multiplexed into a light stream transmitted on a single optical fiber. The inherent optical data rate from a modulated single-mode laser beam traveling through an optical fiber is expected to well exceed 1000 Gbit/sec.
Currently, the practically realizable bandwidth of fiber optical communication systems has been limited by signal conversions between optical and electrical domains and associated electronics hardware. A major component used in the current optical communication systems (e.g., Synchronous Optical Network) is an optical transceiver, a combination of transmitter/receiver in a single package. An optical transceiver can be found in every interface such as a source, a destination or a key interface along an optical network. Besides the applications in optical communications, there are other applications or systems that also use transceivers for receiving or transmitting high-speed data, such as wireless communications devices.
Current transceivers for high-speed signals are built using Silicon Germanium (SiGe), Gallium Arsenide (GaAs), and Indium Phosphorous (InP) processes that have been proved very expensive by current technologies. It is well known that the cost of the processes simply does not make economic sense to implement the transceivers on a large scale. Thus, there is a great need for better designs that can build the transceivers more economically.
This section as well as the abstract of the present invention is for the purpose of summarizing some aspects of the present invention and to briefly introduce one or more preferred embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section and the abstract. Such simplifications or omissions are not intended to limit the scope of the present invention.
The present invention pertains to integrated designs of differential amplifiers that can be used in many electronic circuits and system. It is well known that the parasitic effects in individual components (e.g., transistors and resistors) will introduce artifacts into signals when the frequency of the signals exceeds a certain range. One of the purposes in the present invention is to utilize the parasitic effects in favor to the signals by systematically adjusting the components such that the artifacts are minimized.
According to one aspect of the present invention, a parameter defined as an Electrically Equivalent Geometry or EEG is defined as a function of width and length that confines one part of a transistor controlling how much current can go through. For example, from a layout perspective, an EEG pertains to a physical area of a gate of a MOSFET transistor or to a physical area of an emitter of a bipolar transistor. A proper adjustment of the EEG for each of the transistors in a differential amplifier or circuit can reduce the parasitic effects that can cause the artifacts to the signal but also form inherently resonant filtering functions that minimize harmonic components in the output signals.
To further reduce the parasitic effects that can cause the artifacts to the signal or form proper resonant filtering functions, other individual components, such as resistors, are systematically adjusted. Each of the components is associated with a parameter referred to as an Electrically Equivalent Component Parameter (EECP) that is also inherently a function of a width and a length that define a semiconductor area to make the component. A proper adjustment of EECP for the components, together with the adjusted EEG of the transistors, not only can higher signal speed be accommodated but also the output signals of higher quality can be produced.
To further increase the ability of a differential amplifier or circuit to accommodate even higher signal speed, inductive components (e.g., inductors and transformers) are introduced and systematically adjusted. Inductances from the inductive components can thus further reduce the parasitic effects that can cause the artifacts to the signal or form more proper resonant filtering functions to enhance the signals, resulting in a differential amplifier or circuit with the ability of accommodating even higher signal speed.
There are many benefits, advantages and features in the present invention. One of them is to enable a differential amplifier or circuit to accommodate high signal speed that could not be accommodated in a differential amplifier or circuit that is otherwise designed with the prior art methodology. In essence, the present invention makes it possible to implement high speed systems, such as optical or wireless communications on a large scale with cost-effective semiconductor process (e.g., 0.18xcexcm with complementary metal-oxide semiconductor).